One area of the body which is prone to chronic pain and degeneration of normal function is the hip joint. Whether caused by disease or injury, a portion of the population suffers from ailments relating to the hip. An often utilized solution to problems pertaining to the hip joint is total hip replacement (“THR”) surgery. Generally, THR surgery consists of the replacement of the existing ball and socket of the hip joint with prosthetic replacements. The head of the femur, the ball, is typically removed and replaced with a femoral component made of biocompatible material, which approximately replicates the shape of the original bone. The acetabulum, the socket, is typically reamed and fitted with a prosthetic acetabular cup component that corresponds and cooperates with the femoral component. This prosthetic acetabular cup component often times includes an outer shell constructed of a synthetic material. Typically this shell is in the form of a hollowed out semi-sphere. An insert constructed of plastic, ceramic or metal, is received within the outer shell. The cup may be anchored in the bone through the use of cement. Some cups are press fit in place. Still other cups are held in place by screws or fastening fins or posts integral with the cup itself. A combination of these fastening methods may be employed. Sometimes, owing to the shape of the outer shell and/or the application of compounds that enhance bone growth, the outer shell is designed to foster the growth of bone adjacent the shell. This new bone anchors the cup to the rest of the hip. Total hip replacement surgery has often proven successful in relieving many problems associated with the hip joint.
Total hip replacement surgery is often successful. Nevertheless, it is sometimes necessary to perform the same surgery on the same hip. For example, this may be necessary in situations in which wear or infection degrade the performance of the installed cup and femoral head. This sub-set of total hip replacement surgery is sometimes called revision surgery. In revision surgeries, it may be necessary to remove the acetabular component previously implanted in the acetabulum. As mentioned above, these components may have been cemented in place or otherwise held by bone or fibrous tissue that may have grown in and around the component. The removal of a cup requires the cutting or chipping away of the bone and cement immediately adjacent the cup.
The Inventors' Assignee's U.S. Pat. No. 8,034,059, ACETABULAR SHELL REMOVAL INSTRUMENT, issued 11 Oct. 2011, the contents of which are explicitly incorporated herein by reference, discloses a surgical tool, acetabular cup remover, designed to perform a revision process. As its name implies, this tool is designed to remove an implanted acetabular cup. This tool includes a head that is dimensioned to seat in and rotate in the implanted cup. Plural shafts extend away from this head. A blade is pivotally mounted to one of these shafts. The blade curves forward such that the blade curves around the head. One of the shafts moves longitudinally relative to the head. The blade is connected to this first shaft to pivot as a function of the longitudinal movement of the shaft. A second shaft is rigidly connected to the head. The blade is connected to this second shaft. Axial rotation of this second shaft results in a rotational movement of the blade around an arc. The second shaft is connected to a power tool that oscillates the shaft.
This tool is used by seating the head in the cup that is to be removed. The first shaft is pressed downwardly. This results in the pivoting of the blade against the bone in adjacent the cup. The power tool is actuated. Thus simultaneously the blade is pressed against bone and oscillated in an arc around the cup. The blade shears the bone adjacent the cup. The tool is indexed and the blade pivoted so that the blade forms a cut that extends circumferentially around the portion of the cup embedded in the bone. The formation of this cut separates the cup from the bone in which the cup is embedded. This facilitates cup removal. A new cup is then installed.
The Applicant's PCT App. No. PCT/US2013/028535, ACETABULAR CUP REMOVER WITH INDEXING ASSEMBLY FOR ROTATING THE REMOVAL BLADE AROUND THE CUP, published as WO 2014/133536/US Pat. Pub. No. 2015/0359641 A1, the contents of which are also incorporated herein by reference, disclose a cup remover that has a mechanism for rotating the shaft to which the blade is pivotally attached. This feature reduces the ergonomic strain to which the practitioner is exposed when removing the cup.
The above discussed assemblies are useful for rotating the cup remover blade so the blade moves distally forward and indexing the blade so the blade moves circumferentially around the cup. However to date, the blades designed for use with these tools have not proven to be particularly efficient devices for cutting bone away from the cup to which the tool is fitted.